An electrophotographic image forming apparatus such as a laser printer includes a photosensitive drum on which an electrostatic latent image is formed and a developing apparatus for developing the electrostatic latent image formed on the photosensitive drum.
The developing apparatus includes a case providing a developing chamber and a toner cartridge (a developer cartridge) detachably mounted on the case. A developing roller is rotatably supported in the developing chamber. The peripheral surface of the developing roller is partially exposed from the case, and the exposed portion is in contact with the surface of the photosensitive drum.
The toner cartridge is provided therein with an agitating member for feeding a toner accommodated in the toner cartridge into the developing chamber while agitating the same. The toner fed from the toner cartridge into the developing chamber is carried on the developing roller, and fed from the developing roller to the photosensitive drum while the electrostatic latent image formed on the photosensitive drum is opposed to the developing roller.
As an example of a conventional developing apparatus, there is proposed a developing apparatus having a toner feeding hole and a toner suction hole provided on both axial end portions of a developing roller in a case for connecting a developing chamber and a toner cartridge with each other and an auger member arranged on a position of the developing chamber close to the toner feeding hole and the toner suction hole to extend along the axial direction of a feed roller.
In the developing apparatus, a toner fed into the developing chamber through the toner feeding hole is conveyed along the axial direction of the auger member. The toner in the developing chamber is conveyed along the axial direction of the auger member, and returned to the toner cartridge through the toner suction hole.
However, the toner in the toner cartridge is regularly fed into the developing chamber following rotation of the agitating member. Therefore, the level of the toner in the developing chamber is regularly kept higher than the level of the toner in the toner cartridge. The levels of the toner in the developing chamber and that in the toner cartridge are regularly different from each other, and hence the toner cannot freely move between the developing chamber and the toner cartridge, and it is apprehended that the toner cannot be excellently circulated between the developing chamber and the toner cartridge.
In another conventional developing apparatus, a toner inlet port is formed on a case. On the other hand, a toner outlet port is formed on a toner cartridge. When the toner cartridge is mounted on the case, the toner inlet port and the toner outlet port are opposed to each other, so that the toner cartridge and the case communicate with each other.
The toner cartridge accommodates a toner, while an agitating member is rotatably provided therein. Following rotation of the agitating member, the toner in the toner cartridge is conveyed to a agitating chamber provided in the case through the toner outlet port and the toner inlet port.
An agitator is provided in the agitating chamber. The toner conveyed into the agitating chamber is agitated by the agitator in the agitating chamber, and introduced into the developing chamber.
Following the rotation of the agitating member, however, the toner is directly conveyed from the toner cartridge into the case. Even if the case is filled with the toner, therefore, the toner is continuously fed from the toner cartridge into the case. Consequently, the toner may be excessively fed into the case, and the pressure in the case may be excessively increased. If the pressure in the case is excessively increased, the toner cannot be excellently agitated in the case, and hence the toner may not be normally charged, but may cause reduction of image quality.